The present invention relates to a color reading line sensor having a color filter of a plurality of colors for color-separating a color image.
A conventional color reading sensor comprises a photoelectric transducer element such as a CCD (Charge-Coupled Device). A color filter of a plurality of colors is mounted on the front surface of the photoelectric transducer element to separate the color components. A so-called color reading line sensor having a color reading sensor array is used in a color copying machine or a color facsimile reading unit.
A standard illumination source 2 (FIG. 4) such as a halogen lamp is used as an original illumination light source, and a three-line CCD (FIG. 5) is used as a color original reading line sensor. An R (red) filter element is formed on the first line of the three-line CCD, a G (green) filter element is formed on the second line, and a B (blue) filter element is formed on the third line. A direction A--A' indicates a relative movement direction of the CCD and the original.
Since a spectral distribution of the filter elements is given as shown in FIG. 3, an output from the blue filter element is smaller than those of red and green filter elements A S/N ratio and linearity of the blue filter element are undesirably degraded. In order to solve this problem, two pels (pixels) are assigned to the blue component, and one pel is assigned to each of the red and green components, as described in Japanese Utility Model Laid-Open (Kokai) No. 61-26363. Another example includes two sensor arrays to increase the size of the blue pel area as compared with those of the red and green areas, as described in Japanese Patent Laid-Open (Kokai) No. 62-81163. Still another example is to improve sensitivity by assigning a plurality of pels to all the red, green, and blue components, as described in U.S. Pat. No. 4,264,921.
However, in Japanese Utility Model Laid-Open (Kokai) No. 61-26363, four pels must be used to express one dot, so that the size of each pel is smaller than the conventional pel. Even if two blue pels are given, the sensitivity of other pels (i.e., red and green pels) is degraded as compared with the conventional case. In Japanese Patent Laid-Open No. 62-81163, an output from the blue pels can be increased, but color misregistration undesirably occurs in an output image due to a phase difference between the red and green pels. In U.S. Pat. No. 4,264,921, data of a plurality of pels are used to obtain red, green, and blue outputs, and the number of pels is increased in inverse proportion to the number of pels. Therefore, the overall structure is increased, and transfer time is prolonged. An amplifier may be arranged to increase a blue output. However, noise is also increased. As a result, the result is poorer than the output prior to amplification.